MobileMe/Mail app help please!

My mail app has deleted everything, is now an nonfunctioning mail app. Also my MobileMe contract recently ran out, and i didn't renew it, but if i'm not mistaken that should not effect my local mail app should it?

It just seems that as mobileme has expired so has my mail app. My email address is apparently non existent (as i tried sending from another account and it was unrecognised).

If you have somehow removed a user account, then all your mail messages not moved into folders on your Mac will be lost. Hopefully that hasn't happened and it's just a problem with your email provider.